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'Design' versus '_design_'?

'Design' versus '_design_'?

(OP)
Hi everyone,

I'm brand new to Eng-Tips so if I've posted this in the wrong forum I apologize.

I really came for a bit of advice but first a little bit of context. You see, I'm an engineer intern (not yet licensed) at my company. I'm the only person with engineering background in my department. The idea is that eventually I'll eventually help bring the company to a point where it can do it's own engineering work.

I was working on a simple project and the managers wanted the product to be stamped by a professional. Since I'm not yet a licensed engineer this design would have to be given to a third party to be certified. The project isn't large; <20 k CAD. It's simply a mobile ladder + ramp to access tanker trucks.

On this project I was working with another gentleman. On my first iteration of preliminary calculations I found a starting point for sizing the various beams section sizes, column sizes, etc. As the project went on the design was changed and much of the projects structural components section sizes were changed as well. I was busy with other work so I didn't have time to redo all the preliminary calculations again for all sections. But from what calculations I did redo, without verification through a FEA, I could determine that many sections sizes were likely needlessly large. These sections were changed under no real basis other than, 'they'll be strong enough,' and, 'they'll hold'. I'm not a structural engineer but I do like to read in my off time and the (very) small amount that I did know told me that the way the beams were joint together wasn't optimal But it didn't matter because, 'it was strong enough.'

When I revealed my concerns I was told, 'we don't do engineering design here.'

If you're still with me, this is the result of the project so far...

-We have drawings with sections that are, in my opinion, larger than necessary.
-We have no real calculations or FEA or, what I would consider to be, formal design work.

May I please have your thoughts on what I should do or think in my position?

These are my thoughts so far:

-true, we don't do design work; and we never will if this is our attitude.
-They simply want to ask an engineer to stamp it. I am thinking, if I were the stamping engineer, 'sure let's stamp it. It's obviously over sized so it makes my job easy. It's not my problem if they're wasting material as long as it's strong.'
-If they want to engineer the product then let it be engineered. What they are doing seems very unprofessional. If they don't want it engineered professionally and don't mind the product being over sized, then don't ask for it stamped. Just don't do some weak design in between the two. Because now they're wasting other people's time.
-Let's imagine the time comes and I am able to get a license: of course I won't be able to just stamp anything they push at me. It has to be safe of course.

Any thoughts on the situation? Is this a normal occurance in the workplace?

Thank you for your time

RE: 'Design' versus '_design_'?

1. If you are an intern and not working under the guidance of a licensed engineer, you won't ever become licensed...at least in the US. You must work under a PE/SE as an intern.
2. Oversizing members isn't a sin or a safety issue - it is an ethical issue in that the owner must pay for bigger members than necessary.
3. Final thought: If you want to become a design engineer - find another employer who has PE's under which you can learn.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: 'Design' versus '_design_'?

788456290,

Murphy's Law of Mechanical Engineering: Make it big and forget it.

Over-specifying structure is an alternative to knowing what they are doing. If they don't know what they are doing and they want it light-weight, look out!

--
JHG

RE: 'Design' versus '_design_'?

Remember that the purpose of a PE is public safety. If the design is safe, over-design is irrelevant. The only issue might be if one of these oversized member broke loose and clonked someone on the head, and a smaller member might not have caused as much damage. If the client is OK with the waste, then so be it.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: 'Design' versus '_design_'?

788456290 - Good advice from other members. I'll comment on a different aspect of your question. You mention several times that the structural members are "oversized", "wasteful", etc. These comments indicate that you have complete confidence in the accuracy of the (assumed?) loading on item. This confidence is not always justified. I suggest being cautious if designing precisely to the "theoretical" loads - users have ways of subjecting items to loads that are completely reasonable, but not anticipated by the designer.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: 'Design' versus '_design_'?

often times, engineering economy dictates that certain size beams, pipes are used. Smaller shapes might not be readily available or special order, or they may be hard to work with. For long term serviceability, more robust designs are sometimes necessary. For instance, fatigue sometimes requires larger members than simple moment or shear calculations might indicate. Lack of confidence in fabrication quality might require designing welds much longer than necessary. you might find that was the case for up-sizing the structural elements. And do you really need a FEA to analyze a ladder? Is this a mass produced commercial item?

RE: 'Design' versus '_design_'?

I'll repeat a possibly relevant story here:

A long time ago, between semesters, I worked for a PE who did, well, whatever he could find, around the local paper mills.

He got a new engineer, experienced in aerospace work, but not in mill work, and asked him to design a support for a filter assembly. The assembly comprised two filters (like an oil filter but with a shell big enough to swallow a body), two selector valves and some 8" pipe and fittings.

The new guy took ~3 weeks to design the support, mostly made of 1x1x1/8 angle. It was beautiful, and very light. It couldn't have weighed more than 50 lb. The filter assembly weighed at least 850 lb. dry.

The boss fired the new guy, and told me, junior lead spreader in training, to draw up a similar support, with the tag line, "If you use anything lighter than a W4x13, I'll fire you, too.".

I had seen the new guy's sketches and calculations, all 30+ pages of them, neat and beautiful, so I asked the boss why the new guy's work wasn't adequate.

He said, "What happens, the first time it gets hit by a forklift?". Lesson learned.

Mike Halloran
Pembroke Pines, FL, USA

RE: 'Design' versus '_design_'?

For a one-off design, or where the loads are uncertain, or in-field mods are likely, or the consequences of failure are trivial, then overdesign/design by eye may be a satisfactory way out. The truth is even with millions of dollars of test equipment on cars we often don't know all the loads we need to. (For instance, I am never going to be allowed to take a half million dollar wheel force transducer through a Square Edge Pot Hole at 50 kph).

As to the comment about working directly for a PE - I was under the impression that that is not absolutely required in mech eng due to the small number of mech PEs. Chickens, eggs.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 'Design' versus '_design_'?

Quote:

As to the comment about working directly for a PE - I was under the impression that that is not absolutely required in mech eng due to the small number of mech PEs. Chickens, eggs.

There are cases where a license isn't required if the work is done within a corporation for that corporation - the "industry" exemption.

However, the original poster here implied that they might get a license in the future (quote: "Let's imagine the time comes and I am able to get a license:")

The industrial exemption is there to negate a need to have a licensed PE sign/stamp the work....it doesn't negate the requirements to get licensed in the first place.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: 'Design' versus '_design_'?

"If you are an intern and not working under the guidance of a licensed engineer, you won't ever become licensed...at least in the US. You must work under a PE/SE as an intern." I meant to get licensed.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 'Design' versus '_design_'?

Quote:

...It's simply a mobile ladder + ramp to access tanker trucks...

I think I can imagine what it's like to be on a ladder designed to be just "strong enough". I would get down and ask for a ladder that is "stiff enough" instead. Then my stomach wouldn't flip when I got halfway.

STF

RE: 'Design' versus '_design_'?

If your company 'doesn't do design work', then why is your company designing something?

As others have said, if you're in Ontario and not working directly under a PEng, you'll have a much tougher time getting your PEng.

RE: 'Design' versus '_design_'?

There is also the minor issue of "plan-stamping" being illegal. The PE who signs off on it without doing the design faces all sorts of nasty punishment.

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